The Application of Solar Photovoltaic Power Generation Systems to Rail Transit (Part One)

The Application of Solar Photovoltaic Power Generation Systems to Rail Transit (Part One)


Abstract
The application conditions, principles, composition of solar photovoltaic power generation systems are introduced. A design plan for photovoltaic power generation systems suitable for rail transit is proposed by combining the characteristics of rail transit. Energy, economic, social, and environmental benefit analyses are conducted
 
With the development of the economy and society, energy and environmental issues have gradually attracted social attention, and the use and development of renewable energy has become more and more urgent. With the rapid economic development, China is facing a situation where there are acute shortages of market supplies due to the rapid consumption of electricity, coal, oil and other traditional energy sources. The main constraints on economic and social development are energy consumption and environmental protection. Therefore, rational development and utilization of renewable energy are effective measures to improve the energy structure, enhance the ability to continuously supply energy, ensure energy security, and restore the natural environment.
 
As important renewable energy, solar photovoltaic power generation is one of the most promising new energy technologies recognized in the world today. All developed countries have invested great manpower and material resources in the research and development of this technology, and invested great amounts of money to actively promote the process of industrialization, well develop and cultivate the photovoltaic industry market.
 
There are two main ways to use solar energy. One is photothermal conversion, and the other is photoelectric conversion which is known as photovoltaic power generation. The focus is on the latter. Urban rail transit consumes great amounts of energy and has become a key energy-consuming unit. Using solar photovoltaic power generation to supply power to the electrical loads along the rail transit can not only reduce rail transit's demand for city power and operating costs, but also actively respond to energy saving and emission reduction, effectively promoting the development of new energy.
 
1. The main conditions for using photovoltaic power generation technology
1.1 Sunlight resources
The distribution of solar energy resources is related to the altitude, latitude, climatic conditions and geographical conditions of various places. China has abundant solar energy resources. More than 2/3 of the total area has over 2200 hours of sunshine throughout the year in China. The location for the photovoltaic power generation system requires rich sunlight resources to ensure the stable power generation of the system. In order to facilitate the development and utilization of solar resources, the regions with annual radiation greater than 9260 MJ/m2 are divided into five categories except for western Tibet. The regional classification of solar resources is shown in Table 1.
 
Table 1 Classifications of solar energy resources
Areas Annual sunshine hours/h Annual radiation 1 (M/m2) Main cities
The first area 3200 to 3300 7500 to 9250 Qinghai-Tibet Plateau, northern Gansu, northern Ningxia, southern Xinjiang and other places
The second area 3000 to 3200 5850 to 7500 Northwestern Hebei, southern Inner Mongolia, southern Ningxia, central Gansu, southeastern Tibet, etc.
The third areas 2200 to 3000 5000 to 5850 Shandong, Henan, Southeastern Hebei, Jilin, Yunnan, Southern Guangdong, Southern Fujian, Northern Central Jiangsu and Northern Anhui
The Fourth areas 1400 to 2200 4150 to 5000 Parts of the middle and lower reaches of the Yangtze River, Fujian, Zhejiang, and Guangdong
The fifth areas 1000 to 1400 3350 to 4190 Sichuan and Guizhou provinces
 
1.2 Site conditions
The building and surrounding environment need to be fully considered for the installation of photovoltaic power generation systems in rail transit engineering projects. The following aspects should be paid attention to:
(1) There should be enough areas to install solar panels, storage batteries and other power generation facilities that meet the demand for electricity capacity.
(2) Avoid or stay away from anything which can shade for the layout of photovoltaic modules.
(3) The place should be close to the main power grid to reduce the investment in new transmission lines.
 
2. The design of the photovoltaic power generation system of rail transit
According to the construction form of rail transit engineering, places which can install photovoltaic power generation systems mainly include ceilings of elevated stations (ground stations), ceilings of entrances and exits of stations and ceilings of car depots. Since the roof space of the car depot warehouse is relatively large and wide, it is suitable for installing large-scale photovoltaic power generation systems. The car depot is taken as an example to introduce the design scheme of the solar photovoltaic power generation system applied in rail transit engineering in this article.
 
2.1 The selection of the solar cell
Solar cells are the basic components of photovoltaic modules. The main types are monocrystalline silicon, polycrystalline silicon, amorphous silicon and thin-film cells. Monocrystalline silicon cells and polycrystalline silicon cells are the mainstream products on the current market; the monocrystalline silicon cell has the highest photoelectric conversion rate. The conversion efficiency of commercial cells can reach 15% to 19%, and the performance is stable; solar cell modules with the same capacity requires a small installation area and relatively high costs; the production efficiency of polycrystalline silicon cells is high, and the photoelectric conversion efficiency is slightly lower than that of monocrystalline silicon. The conversion efficiency of its commercial cells is 13% to 16%, and there is a certain reduction in the conversion efficiency during the service life of the product. The cost for polycrystalline silicon cells is relatively low. The service life of monocrystalline silicon cells and polycrystalline silicon cells can reach 25 years, and the power attenuation during the service period can be less than 20%.
 
With the continuous advancement and development of the photovoltaic industry and the continuous improvement of material technology, comprehensive production costs will gradually decrease. Monocrystalline silicon solar cell modules with high photoelectric conversion efficiency, stable performance, and mature technology are chosen to introduce the program.